In research and manufacturing, it is often important to accurately position an object relative to another object. In doing this positioning, the sensing techniques used include capacitive sensing, interference techniques, strain sensors, avalanche photo diodes, and atomic force microscopes. Generally these techniques are expensive, do not positively identify when the correct position has been achieved, are not sufficiently accurate, and are inconvenient for use in vacuum deposition systems. Systems based on these techniques may also use sensors that are too large to be placed on small objects.
Mad City Labs (http://www.madcitylabs.com/) has a positioning system that uses a near field transducer (NFT) to radiate a small area with an evanescent field from a laser. NFTs have small apertures of size d<Δ, the wavelength of the laser, that permit the light to pass a distance of about d/2 beyond the aperture. However, since d<Δ one can use NFTs to illuminate very small regions. Lasers and NFTs have been used previously in heat assisted magnetic recording (HAMR) to heat the magnetic media to 700° C. and in near field scanning microscopes. Heating the media reduces its coercivity so that it can be written using a smaller write magnetic field. In these applications, there is no sensor that is fabricated on the object that is illuminated by the evanescent field.
It can be seen by a person having ordinary skill in the art that the PRIOR ART systems have drawbacks.